Strain relief mechanism for a plasma arc torch

ABSTRACT

The present invention relates to a strain relief mechanism for a plasma arc torch. In particular, the invention relates to a strain relief system including a positive axial restraint component for restraining axial movement of a lead relative to a housing and a positive rotational restraint component for restraining rotational movement of the lead relative to the housing, wherein the positive axial restraint component and the positive rotational restraint component are independent components arranged in a spaced relationship relative to each other.

FIELD OF THE INVENTION

[0001] The invention relates to a strain relief mechanism for a tool. Inparticular, the invention relates to a strain relief mechanism for aplasma arc torch which includes a positive axial restraint component anda positive rotational restraint component.

BACKGROUND OF THE INVENTION

[0002] Plasma arc torches are widely used in the cutting or marking ofmetallic materials. A plasma torch generally includes an electrode and anozzle having a central exit orifice mounted within a torch body,electrical connections, passages for cooling and arc control fluids, aswirl ring to control fluid flow patterns in the plasma chamber formedbetween the electrode and nozzle, and a power supply. The torch producesa plasma arc, which is a constricted ionized jet of a gas with hightemperature and high momentum. Gases used in the torch can benon-reactive (e.g. argon or nitrogen), or reactive (e.g. oxygen or air).

[0003] In operation, a pilot arc is first generated between theelectrode (cathode) and the nozzle (anode). Generation of the pilot arcmay be by means of a high frequency, high voltage signal coupled to a DCpower supply and the torch or any of a variety of contact startingmethods.

[0004] One known configuration of a plasma arc torch includes one ormore leads connecting the torch to the power supply to provide the torchwith electrical current and gas. The connection of the lead(s) to thepower supply must be rugged to handle the strain placed on the lead asit is manipulated in order to place the plasma arc torch in a positionto cut or mark a workpiece. While most operators of hand-held systemsuse the plasma arc torch, lead and power supply properly, some operatorshave used the lead for purposes not intended by the manufacturer (e.g.stepping on the lead(s) or even pulling the lead(s) to drag the powersupply to a new location).

[0005] The lead(s) used to connect the torch to the power supply can bea single integral lead having a gas hose located in the middle of thelead and electrical conductors and fillers arranged symmetrically aroundthe gas hose. A jacket material is extruded over the gas hose,electrical conductors and fillers. A strain relief mechanism can beattached to the jacket to handle loads applied to the lead. The jacket,gas hose, electrical conductors and fillers are anchored together over abarb-type fitting. A clamp, which acts as the strain relief mechanism,is applied to grab and hold the jacket to prevent relative axial motion(or twisting) of the lead components. The stress through the lead isabsorbed by the clamp and transferred to the chassis of the power supplythrough a mechanical connection.

[0006] One example of an integral lead with a clamp which prevents axialmotion or twisting of lead components is found in the lead used in thePMX900/PAC 125 plasma arc torch system manufactured by Hypertherm, Inc.The lead used in this plasma arc torch system is connected to the powersupply by a threaded quick disconnect connector. A quick disconnectconnector is advantageous in that it simplifies torch removal but isexpensive to make. Another example of an integral lead with a clamp forpreventing axial motion (or twisting) of lead components can be found inthe lead used in the PMX600/PAC123 plasma arc torch system manufacturedby Hypertherm, Inc. In this system, stress is absorbed by the chassis ofthe power supply through a tool-tightened nut. A tool-tightened nut isadvantageous in that it is inexpensive, but the tool-tightened nutrequires the use of a tool. The use of a tool can be time consuming, andthe tool can be easily misplaced.

[0007] It is therefore an object of the present invention to provide animproved and inexpensive axial and rotational strain relief mechanismfor connecting a lead to a plasma arc torch power supply.

SUMMARY OF THE INVENTION

[0008] In one aspect, the invention features a strain relief system forrestraining a lead relative to a housing. The strain relief systemincludes a positive axial restraint component for restraining axialmovement of the lead relative to the housing and a positive rotationalrestraint component for restraining rotational movement of the leadrelative to the housing. The positive axial restraint component and thepositive rotational restraint component are independent componentsarranged in a spaced relationship relative to each other. In oneembodiment, the positive axial restraint component comprises a quickdisconnect connector and the positive rotational restraint componentcomprises a shaped boot attached to the lead.

[0009] In another aspect, the invention features a plasma arc torch forpiercing or cutting a workpiece. The plasma arc torch includes a torchbody, a power supply, a lead with two ends. The first end of the lead isconnected to the torch body, and the second end of the lead is attachedto a strain relief system to couple the lead to the power supply. Thestrain relief system includes a positive axial restraint component forrestraining axial movement of the lead relative to the power supply anda positive rotational restraint component for restraining rotationalmovement of the lead relative to the power supply. The positive axialrestraint component and the positive rotational restraint component areindependent components arranged in a spaced relationship relative toeach other.

[0010] In another aspect, the invention features a method forrestraining a lead relative to a housing. The method includes the stepsof providing a positive axial restraint component for restraining axialmovement of the lead relative to the housing, and providing a positiverotational restraint for restraining rotational movement of the leadrelative to the housing, and connecting the lead to the housing. Thepositive axial restraint component and the positive rotational restraintcomponent are independent components arranged in a spaced relationshiprelative to each other.

[0011] In yet another aspect, the invention features a method forrestraining a lead relative to a power supply for a plasma arc torch.The method includes the steps of providing a positive axial restraintcomponent for restraining axial movement of the lead relative to thepower supply and providing a positive rotational restraint component forrestraining rotational movement of the lead relative to the powersupply. The positive axial restraint component and the positiverotational restraint component are independent components. The methodalso includes the step of arranging the positive axial restraintcomponent and the positive rotational restraint component in a spacedrelationship relative to each other along a longitudinal axis of thelead. Further, the method includes the step of connecting the lead tothe power supply for the plasma arc torch.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a diagram of a strain relief system used to connect alead to a housing.

[0013]FIG. 2 is a diagram of a plasma arc torch power supply, lead and atorch body used for cutting or piercing a metal workpiece.

[0014]FIG. 3 is a schematic cross-sectional view of a conventionalplasma arc torch.

[0015]FIG. 4 is a cross-section view of the lead from FIG. 2.

[0016]FIG. 5 is a diagram of a lead, shaped boot, and quick disconnectconnector.

[0017]FIG. 6 is a diagram of a lead attached to a plasma arc torch powersupply.

[0018]FIG. 7 is a cross-section along a longitudinal axis of the leadattached to the plasma arc torch power supply from FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

[0019]FIG. 1 illustrates a strain relief system which connects a lead toa housing. The strain relief system 10 prevents axial movement androtational displacement of the lead 12 relative to the housing 14. Thestrain relief system 10 includes a positive axial restraint component 16for restraining axial movement of the lead 12 relative to the housing 14and a positive rotational restraint component 18 for restrainingrotational movement of the lead 12 relative to the housing 14. Thepositive axial restraint component 16 and the positive rotationalrestraint component 18 are independent components arranged in a spacedrelationship relative to each other.

[0020] In one embodiment, the positive axial restraint component 16 caninclude a quick disconnect connector 22 attached to the lead 12. Inanother embodiment, the positive axial restraint component 16 caninclude the quick disconnect connector 22 and a quick disconnectconnector receptacle 17 positioned inside the housing 14.

[0021] In one embodiment, the positive rotational restraint component 18can include a shaped boot 24 attached to the lead 12. In anotherembodiment, the positive rotational restraint component 18 can includethe shaped boot 24 and a mating receptacle 28 formed in the housing 14.The shaped boot 24 and the mating receptacle 28 are designed to preventrotation of the lead 12 when the shaped boot 24 is inserted in themating receptacle 28. The shaped boot 24 and mating receptacle 28 aredesigned to have anti-rotation features 25 a, 25 b, 25 a′, and 25 b′ toprevent rotation of the lead 12 relative to the housing 14.

[0022] The positive axial restraint component 16 and the positiverotational restraint component 18 are arranged in a spaced relationshiprelative to a longitudinal axis 20 of the lead 12. In addition, thepositive axial restraint component 16 and the positive rotationalrestraint component 18 can be configured so that both are engagedsimultaneously when the lead 12 is connected to the housing 14.

[0023] Generally, the strain relief system 10 can be useful in a varietyof tools. However, it has been found that the strain relief systemdescribed herein is particularly useful in a plasma arc torch system.

[0024]FIG. 2 illustrates a plasma arc torch system representative of anyof a variety of models of torch systems. A power supply 60 providescontinuously variable current output within a range (e.g. from about 20to 40 amperes). This range can be lower or higher depending on the torchsystem, the thickness the workpiece and the desired cutting speeds. Thevariable power supply allows for wide variations in cutting speeds for agiven thickness of metal.

[0025] A torch body 62 configured for hand cutting is connected to thepower supply 60 by a lead 12. The power supply 60 is enclosed by housing14. The lead 12 is connected to the power supply 60 by a strain reliefsystem 15. The lead 12 provides the torch body 62 with a plasma gas froma gas source (not shown) and electrical power from the power supply 60to ignite and sustain a plasma stream. In one embodiment, air is used asthe plasma gas, but other gases can be used to improve cut quality onmetals such as stainless steel and aluminum. A workpiece lead 66provides a return path for the current generated by the power supply 60and is typically connected to a workpiece (not shown) by a clamp 68.

[0026]FIG. 3 illustrates in simplified schematic form a plasma arc torchrepresentative of any of a variety of models of torches. The torch has abody 70 which is generally cylindrical with an exit orifice 72 at alower end 74. A plasma arc 76, i.e. an ionized gas jet, passes throughthe exit orifice 72. The torch is used to pierce and cut metal, such asmild steel or other electrically-conducting materials, in a transferredarc mode. In cutting mild steel, the torch operates with a reactive gas,such as oxygen or air, or a non-reactive gas, such as nitrogen or argon,as the plasma gas to form the transferred plasma arc.

[0027] The torch body 70 supports an electrode 89 having an insert 88 inits lower end and a nozzle 78 spaced from the electrode 89. The nozzle78 has a central orifice that defines the exit orifice 72. A swirl ring80 is mounted to the torch body 70. In one embodiment, the swirl ring 80has a set of radially offset (or canted) gas distribution holes 82 thatimpart a tangential velocity component to the plasma gas flow causing itto swirl. This swirl creates a vortex that constricts the arc andstabilizes the position of the arc on the insert.

[0028] In operation, the plasma gas flows through a gas inlet tube 84and the gas distribution holes 82. The gas flows into the plasma chamber86 and out of the torch through the exit orifice 72. A pilot arc, whichionizes the gas passing through the exit orifice, is first generatedbetween the electrode 88 and the nozzle 78. The arc then transfers fromthe nozzle to a workpiece 90. It is noted that the particularconstruction details of the torch body, including the arrangement ofcomponents directing of gas and cooling fluid flows and providingelectrical connects, can take a wide variety of forms.

[0029] When repairing or replacing the torch head 74 or lead 12, it isimportant that the lead connected between the torch and the power supplycan be disconnected from the power supply. In addition, operators oftenwish to disconnect the torch from the power supply for convenienceduring storage or transport of the system.

[0030]FIG. 4 illustrates a cross-section of the lead 12 (Section A-Afrom FIG. 2) used to supply current and gas to the torch body 62. Thelead 12 has wires 30 for delivery of current from the power supply 60 tothe torch body 62. In addition, a hose 32 delivers gas from the powersupply to the torch body. In one embodiment, the hose 32 is centrallylocated within the lead 12. In another embodiment, the hose 32 is notlocated in the center of lead 12. In still another embodiment, there canbe more than one hose 32 in lead 12. The wires 30 and hose 32 arelocated inside of a jacket 34. Fillers 36 are disposed in remainingspaces inside the jacket 34 to provide support and fill in empty space.

[0031]FIG. 5 illustrates the lead 12 and the shaped boot 24. The lead 12also includes a quick disconnect connector 22. The quick disconnectconnector 22 can be connected to the quick disconnect connectorreceptacle 17, which in one embodiment is secured within the housing 14(FIG. 1) of the power supply 60. The quick disconnect connector 22 alsofunctions as a gas fitting to allow gas or fluid to be transferred fromthe power supply 60 to the torch body 62 via lead 12. Wires 30 canextend through holes 38 to connect the wires 30 with an electricalconnector in the power supply 60 (FIG. 6).

[0032]FIG. 6 illustrates the portion of the lead 12 connected to thepower supply 60. The lead 12 has a longitudinal axis 20. The leadfurther includes the shaped boot 24 molded over the jacket 34. Themating receptacle 28 and shaped boot 24 are both compatibly shaped toallow the shaped boot 24 to fit securely within the mating receptacle 28and have anti-rotation features 25 a, 25 b, 25 a′ and 25 b′ to preventrotation of the lead 12 relative to the housing 14.

[0033] As shown in FIG. 6, the lead 12 is connected to the quickdisconnect connector receptacle 17 located in the housing 14 of powersupply 60. FIG. 7 is a cross-section (Section B-B from FIG. 6) takenperpendicular to the longitudinal axis 20 of lead 12 and illustrates theconnection of lead 12 to the quick disconnect connector receptacle 17.The embodiment shown uses the quick disconnect connector receptacle 17,which engages the quick disconnect connector 22. The quick disconnectconnector 22 also acts as gas fitting, allowing gas or fluid to besupplied with the lead 12 from the power supply to the torch body 62.The foregoing are merely representative embodiments, as otherconfigurations are possible and within the scope of the inventions.

[0034] Equivalents

[0035] While the invention has been particularly shown and describedwith reference to specific preferred embodiments, it should beunderstood by those skilled in the art that various changes in form anddetail may be made therein without departing from the spirit and scopeof the invention as defined by the appended claims.

What is claimed is:
 1. A strain relief system for restraining a leadrelative to a housing, the system comprising: (a) a positive axialrestraint component for restraining axial movement of the lead relativeto the housing; and (b) a positive rotational restraint component forrestraining rotational movement of the lead relative to the housing,wherein the positive axial restraint component and the positiverotational restraint component are independent components arranged in aspaced relationship relative to each other.
 2. The strain relief systemof claim 1 wherein the positive axial restraint component and thepositive rotational restraint component are arranged in a spacedrelationship relative to a longitudinal axis of the lead.
 3. The strainrelief system of claim 1 wherein the positive axial restraint componentand the positive rotational restraint component are configured so thatboth are engaged simultaneously when the lead is connected to thehousing.
 4. The strain relief system of claim 1 wherein the positiveaxial restraint component comprises a quick disconnect connector.
 5. Thestrain relief system of claim 4 wherein the positive axial restraintcomponent further comprises a quick disconnect connector receptacle. 6.The strain relief system of claim 1 wherein the positive rotationalrestraint component comprises a shaped boot attached to the lead.
 7. Thestrain relief system of claim 6 wherein the positive rotationalrestraint component further comprises a mating receptacle in the housingfor accepting the shaped boot.
 8. The strain relief system of claim 1wherein the positive axial restraint component comprises a quickdisconnect connector and the positive rotational restraint componentcomprises a shaped boot attached to the lead.
 9. The strain reliefsystem of claim 1 wherein the lead comprises a fluid line and at leastone electrical conductor.
 10. The strain relief system of claim 9further comprising an electrical connection connecting the at least oneelectrical conductor with a mating connector in the housing.
 11. Thestrain relief system of claim 9 wherein the fluid line is generallycentrally disposed in the lead and the at least one electrical conductoris disposed radially outwardly therefrom.
 12. A plasma arc torch forpiercing or cutting a workpiece, the torch comprising: a torch body; apower supply; a lead comprising a first end connected to the torch bodyand a second end; and a strain relief system to couple the second end ofthe lead to the power supply, wherein the strain relief systemcomprises: (a) a positive axial restraint component for restrainingaxial movement of the lead relative to the power supply; and (b) apositive rotational restraint component for restraining rotationalmovement of the lead relative to the power supply, wherein the positiveaxial restraint component and the positive rotational restraintcomponent are independent components arranged in a spaced relationshiprelative to each other.
 13. The torch of claim 12 wherein the positiveaxial restraint component and the positive rotational restraintcomponent are arranged in a spaced relationship relative to alongitudinal axis of the lead.
 14. The torch of claim 12 wherein thepositive axial restraint component and the positive rotational restraintcomponent are configured so that both are engaged simultaneously whenthe lead is connected to the power supply.
 15. The torch of claim 12wherein the positive axial restraint component comprises a quickdisconnect connector.
 16. The torch of claim 15 wherein the positiveaxial restraint component further comprises a quick disconnect connectorreceptacle.
 17. The torch of claim 12 wherein the positive rotationalrestraint component comprises a shaped boot attached to the lead. 18.The torch of claim 17 wherein the positive rotational restraintcomponent further comprises a mating receptacle in the power supply foraccepting the shaped boot.
 19. The torch of claim 12 wherein thepositive axial restraint component comprises a quick disconnectconnector and the positive rotational restraint component comprises ashaped boot attached to the lead.
 20. The torch of claim 12 wherein thelead comprises a fluid line and at least one electrical conductor. 21.The torch of claim 20 further comprising an electrical connectionconnecting the at least one electrical conductor with a mating connectorin the power supply.
 22. The torch of claim 20 wherein the fluid line isgenerally centrally disposed in the lead and the at least one electricalconductor is disposed radially outwardly therefrom.
 23. A method forrestraining a lead relative to a housing, the method comprising thesteps of: (a) providing a positive axial restraint component forrestraining axial movement of the lead relative to the housing; (b)providing a positive rotational restraint component for restrainingrotational movement of the lead relative to the housing, wherein thepositive axial restraint component and the positive rotational restraintcomponent are independent components arranged in a spaced relationshiprelative to each other; and (c) connecting the lead to the housing. 24.The method of claim 23 wherein the positive axial restraint componentand the positive rotational restraint component are arranged in a spacedrelationship relative to a longitudinal axis of the lead.
 25. The methodof claim 23 wherein the positive axial restraint component and thepositive rotational restraint component are configured so that both areengaged simultaneously when the lead is connected to the housing. 26.The method of claim 23 wherein the positive axial restraint componentcomprises a quick disconnect connector.
 27. The method of claim 26wherein the positive axial restraint component further comprises a quickdisconnect connector receptacle.
 28. The method of claim 23 wherein thepositive rotational restraint component comprises a shaped boot attachedto the lead.
 29. The method of claim 28 wherein the positive rotationalrestraint component further comprises a mating receptacle in the housingfor accepting the shaped boot.
 30. The method of claim 23 wherein thelead comprises a fluid line and at least one electrical conductor. 31.The method of claim 30 wherein the fluid line is generally centrallydisposed in the lead and the at least one electrical conductor isdisposed radially outwardly therefrom.
 32. The method of claim 30wherein the method further comprises the step of: (d) connecting the atleast one electrical conductor to a mating connector in the housing. 33.A method for restraining a lead relative to a power supply for a plasmaarc torch, the method comprising the steps of: (a) providing a positiveaxial restraint component for restraining axial movement of the leadrelative to the power supply for the plasma arc torch and a positiverotational restraint component for restraining rotational movement ofthe lead relative to the power supply for the plasma arc torch, whereinthe positive axial restraint component and the positive rotationalrestraint component are independent components; (b) arranging thepositive axial restraint component and the positive rotational restraintcomponent in a spaced relationship relative to each other along alongitudinal axis of the lead; and (c) connecting the lead to the powersupply for the plasma arc torch.